I don't know if Peter Arno gets enough love nowadays, his work is fascinating to study.
R.C. Harvey credited him with inventing (or rediscovering, for you Rodolphe Töpffer fans) the modern print cartoon, a form where the gag or story point is carried through text/picture interdependence. "Well, back to the old drawing board" contains no humorous content in of itself, but combined with the above image makes for a classic and oft-sited gag.
For some reason, Arno drew a hell of a lot of boob jokes. I could do a whole series of post about Peter Arno and boob jokes. I love this one because the entire situation is based on a subtle change of eye-line (aided by the gentleman's very arrow-like nose pointing to what he's admiring).
Forget punchlines, this gag is just pure character. Even in a style with a strict economy of detail, Arno expresses a wealth of character information with carefully chosen costume bits, a choice piece of buisness and a helluva gesture and facial expression.
Look at this Major! Even when he's harassing this guy's wife, he's standing ramrod straight. This could have been a passionate dip-kiss, but it's certainly more unique and true to character the way this soldier's kissing the woman so...militantly.
He can't be using more than 5 values in any of these examples, but boy does he make them work! I love this vertical rhythm set up with the whites of the uniforms.
Even if the gag itself isn't that funny, Arno's cartoons are just fun to look at. Design-wise, they're a treat. His characters, though simple, are expressive as hell, look at how the pair above are interacting, you know exactly what going on in both their heads. His sense of character, staging and dynamic rendering style really make for appealing drawing.
Arno's sense of composition is pretty damned awesome, particularly using the left to right reading convention as an aid to communicating the gag, either working with it to enhance movement, working against it for specific effect (look how put upon that little kid looks with the right-to-left man lecturing him) or keeping the "punchline" element of the composition to the right so it will be "read" last, like below.
I think most of the great New Yorker cartoonists were deeply disturbed people, and I love 'em for it.